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Capture the CO₂ emitted by a steel factory and combine it with green hydrogen to turn the waste gas into fuel on the spot. That is in short the aim of the four-year C2FUEL-project, in which companies from all over Europe collaborate with academics from DTU, Laboratoire Réactions et Génie des Procédés and TU Eindhoven.

‘C2FUEL is led by ENGIE, a French energy company dedicated to the energy transition,’ tells Fernanda Neira D’Angelo, one of the ¹û¶³´«Ã½â€™s researchers who coordinates  the ¹û¶³´«Ã½â€™s reactor design efforts in the project. The aim is to develop energy-efficient, economically and environmentally viable CO₂ conversion technologies which are to be demonstrated at Dunkirk between a DK6 combined cycle power plant, the Arcelor Mittal steel factory and one of the major European harbors. The idea is to selectively remove the carbon dioxide present in the blast furnace flue gas and combine it with green hydrogen generated by electrolysis fed with renewable electricity to produce two promising energy carriers.

‘The aim of the C2FUEL-project is to produce both formic acid and dimethyl ether,’ chemical engineer Neira D’Angelo explains. Dimethyl ether is already known as an alternative diesel-like fuel for trucks and ships. Formic acid is a promising substance to carry hydrogen, which can be used as a fuel as well.  Now, the focus is on scaling up the production of dimethyl ether.

Low value molecule
Though the reaction of hydrogen and carbon dioxide to dimethyl ether is not entirely new, several scientific challenges had still to be overcome, Neira D’Angelo explains. ‘Converting carbon dioxide is far from easy. It is a fully oxidized molecule, which has no heat value or functionality whatsoever. It is what we call a low value molecule, meaning that you need to introduce a lot of energy to be able to do anything useful with it. That energy is now coming from hydrogen, which is a very valuable molecule. One of the biggest challenges in CO₂ conversion therefore is how to develop environmentally advantageous and economically competitive technologies.’

In terms of reactor design, which is the part of the project ¹û¶³´«Ã½ is responsible for, one of the biggest challenges is that the chemical reaction is thermodynamically limited. ‘During the reaction a lot of water is produced, which deactivates the catalyst and limits the conversion. Therefore we had to come up with solutions to remove the water from the reaction.’ That is easier said than done, the chemical engineer explains. ‘For this specific application, a membrane reactor is the most suitable candidate. However, if you use an ordinary membrane, chances are that hydrogen will also go through.’ Eventually, together with project partner Tecnalia, ¹û¶³´«Ã½ researchers developed a stable membrane that is selective for water only. ‘We have tested our membranes first at lab scale to see what would be the optimal composition, how to produce them at larger scale, and how their performance is affected by different reaction cycles. Project partner Tecnalia has then produced the membranes at the required scales.’

Conversion of renewable feedstock
For Neira D’Angelo, this project fits seamlessly into her line of research at ¹û¶³´«Ã½. ‘I work on reactor engineering for the conversion of renewable feedstock into useful products. In all of my work, I try to understand the interplay between the chemical reaction, the materials used in the catalyst, and the transport phenomena and thermodynamics at play in the reactor.’ To unravel the complex puzzle of all parameters that influence the eventual efficiency and productivity of the reactor, Neira D’Angelo follows a systematic approach. ‘We always start from the chemistry. So first we take a lab-scale reactor where transport does not play a significant role to study the mechanism of the reaction. Then, we design experiments to isolate specific parts of the system to study the influence of different parameters, in order to establish the requirements for our larger-scale reactor. Based on those, we choose a reactor concept, ranging from micro-reactors and membrane technology to spinning discs. And with the help of phenomenological reactor models that we develop, we then predict the behavior of the reactor at the required scales.’

As far as the C2FUEL-project goes, Neira D’Angelo is optimistic about the expected results. Though the true proof of the pudding will be in the eating, the chemical engineer is confident that the final reactor will do what it is supposed to do. ‘Currently we are building a scaled up version of our lab-scale reactor in a container, which will be shipped to Dunkirk sometime next year.’

Solving bottlenecks
When looking at the energy transition in a broader sense, one of the most uplifting characteristics of the C2FUEL-project is that the technology that has been developed is not process specific, and thus can also be of use for other applications. ‘All in all, I think technology is not the major bottleneck when it comes to using CO₂ as a feedstock for fuels. Of course, there are still some technical issues to solve, but we have shown already that this is feasible. The biggest problem is the economic side of things. One of the main tasks I see for us as researchers is to develop solutions with increased performance to drastically reduce costs.’